1. Field of the Invention
The present invention relates to a method of brazing ceramic surfaces, in particular a method for producing a brazed joint with metal/ceramic joints or ceramic/ceramic joints, whereby at least one of the ceramic surfaces to be brazed is structured before brazing by the insertion of bores.
2. Discussion of Background Information
A method for producing a brazed joint with metal/ceramic composite materials or ceramic/ceramic composite materials is already known from EP 0 476 772, whereby before brazing at least one of the ceramic surfaces to be brazed is structured before brazing with the aid of a laser by the insertion of conical bores with uniform diameter, uniform depth and with uniform spacing between the bores. The bores thereby feature an average diameter in the range of 50 μm to 500 μm and a depth in the range of 100 μm to 2 mm. However, this method has certain disadvantages, which will be explained in detail below.
An important influencing factor for the usability of ceramic/ceramic joints or metal/ceramic joints is a mechanically good substance-locking joint between the individual components and in many cases one that is resistant to high temperatures. Since the materials to be joined often have very different coefficients of thermal expansion, induced stress conditions occur after the joining process and during stressing which impair, and in extreme cases even destroy, the strength of the joint zone.
In order to optimize the strength of such a joint zone, in particular the surface of the ceramic material can be enlarged. This can be achieved by surface structuring, such as inserting grooves or channels by mechanical processing. However, this measure is not always sufficient to ensure sufficient strength of the brazed joint. No significant increase in strength can be observed, either, through enlarging the brazed surface by the insertion of through bores with inserted grooves on the ceramic surface, due to the low number of bores and the bore dimensions. Inserting non-through bores in ceramic material has proven to be more advantageous and can also be used in particular within the scope of the present invention.
The method of EP 0 476 772 is disadvantageous on the one hand because with the dimensions given there the structuring expenditure is very high and there is a danger that due to the selected dimensions an adequate filling of the bores with brazing material cannot always be guaranteed. In particular for fiber-reinforced ceramics with a two-dimensional layer structure of the fibers, thus with a typical laminate structure, a further problem results that during stress the shearing strains in the laminate become too high and the fiber-reinforced ceramic component fails in an interlaminar manner. This can be prevented only to a limited extent by the layout of the bores given in EP 0 476 772.